The present invention relates to a drive shield for use in driving or excavating tunnels, adits, galleries and similar cavities and hereinafter referred to as a tunnel or tunnels for convenience.
Known forms of drive shields are composed of a series of sharp-ended plank-like drive members arranged side-by-side in contact with the tunnel wall and supported for longitudinal displacement in the advancing direction by a frame. The pressure exerted on the drive members by the tunnel wall usually varies around the wall and over zones along the tunnel. It is known to sub-divide a drive shield into two parts each part being composed of at least one expandable ring and a group of drive members carried thereby. Such a construction is described in German specifications 2,314,703 and 2,144,862. The drive members of the parts are interspersed to provide the usual cylindrical shell contacting the tunnel wall and either shield part can be firmly braced against the wall by expanding the appropriate ring. Rams serve to alternately shift one drive shield part in relation to the other. With such a construction it is not possible to shift individual drive members nor is it possible to brace selected members against part of the tunnel wall with increased force relative to the other members.
A general object of the present invention is to provide an improved drive shield.